Skeletal Muscle Contraction Flashcards
Skeletal muscle composed of
fascicles that are in turn comprised of multinucleated muscle fibers
Z line
marks the boundary between two sarcomeres
I band
contains only the actin thin filaments, which extend from the Z line towards the center of the sarcomere
A bank
myosin thick filaments
H zone
no overlap between actin and myosin
M line
center of the sarcomere and is the site at which the thick filaments are linked with each other
sliding filament theory
thick and thin filaments slide past each other during muscle contraction
Z line moves closer together, length of A band is constant, length of I band shortens, as sarcomere shortens, so does the muscle
myosin molecule
has six polypeptide chains, 2 heavy chains and 4 light chains forming 2 globular heads and one double coiled helix known as the tail
myosin heavy chain
globular region that binds actin and hydrolyzes ATP during muscle contraction. also contains the hinge region and extended tail region. two heavy chains are wound together in each myosin molecule.
sarcoplasmic reticulum
stores and releases calcium. works with T tubules to ensure sarcomeres contract together within a muscle fiber.
T tubule
action potentials propagate along plasma membrane and down into T tubules to cause SR to release calcium. works with SR to ensure sarcomeres contract together within a muscle fiber.
tropomyosin
alpha helical protein that covers the myosin binding sites on the thin filament in resting muscle. blocks myosin from binding to the thin filament.
Troponin
complex of three protein subunits: troponin C binds calcium, troponin I has a strong affinity for actin, and troponin T binds to tropomyosin.
troponin complex binds tropomyosin to the thin filament
latent period
between stimulation and contraction. time delay between action potential and activation of the crossbridge cycle.
twitch
contraction generated by single action potential. basis of muscle contraction. heart contracts by twitch only.
